1. Field of the Invention
The present invention is directed to a computer tomography apparatus, and in particular to a computer tomography apparatus of the type for conducting a spiral scan.
2. Description of the Prior Art
The number of applications wherein many individual image must be prepared is increasing with the increasing significance of the spiral scan technique in computer tomography. Included among these applications is the production of three-dimensional reformations from many planar images or cine representations. The calculating and time outlay of an algorithm for the reformations becomes an important consideration of view under these circumstances. The number of convolution/back-projection operations required overall for calculating a desired plurality of images is considered a measure of this outlay.
When one wishes to calculate images at a distance of N.sub.s slice thicknesses d a spacing d/n with conventional spiral technique, i.e. nN.sub.s images, then nN.sub.s N.sub.2.pi. convolution/back-projection operations are required for this purpose (N.sub.2.pi. =number of projections onto 2.pi.). High values can be achieved dependent on the selection of the parameters. There is therefore great interest in methods that resolve this task quickly and without image quality losses.
European Application 0 504 855 discloses one possibility of making the image calculation faster on the basis of a recursive method for a spiral algorithm that requires data from the region of two entire slice thicknesses for the calculation of an image. The image quality, however, suffers thereby, particularly the resolution in the direction of the patient axis.